Heisei Nenkin Gekijou: Erodake

Main character is a poor student who has to go for part-time job to support himself. His payment gets delayed for a week, so he is on the brink of starvation when he finds a jar with mysterious mushrooms in his room. After he eats such a mushroom, he suddenly feels very horny. Just imagine what effect it would have on the girls he cares about!

[From vndbreview]